It has previously been proposed to provide a contact-less transducer and pulse generating system for internal combustion engines in which two transducer elements are coupled to a rotary magnetic component, driven from the engine (see German disclosure document DT-OS No. 2 425 595). The arrangement described has been used to change the ignition instant, that is ignition timing in dependence on speed. The pulse provided by that system is used only to trigger the ignition event. The pulse length is constant relative to the angle of rotation through which the rotary portion of the transducer passes.
Rotary pulse generating systems which are designed primarily to provide an output pulse at a predetermined instant to trigger an ignition frequently provide the pulse only with respect to a predetermined angle of rotation, or rotary position of a rotating element of the engine, for example the crankshaft thereof. If the pulse is simultaneously to be used to close the ignition circuit, to provide electrical energy to a spark coil, then, as the speed of the engine increases, lesser energy can be stored in the ignition coil. Thus, the energy available to trigger the spark becomes less and less, as speed increases, if the closing time of the trigger circuit is proportional to engine speed.